The present invention relates to a brake pressure control system, in particular, to an anti-locking control system, for use with brake systems of automotive vehicles comprising two brake actuating circuits preferably disposed in diagonal relationship, with each of such circuits hydraulically actuating at least one wheel brake cylinder of the front axle and at least one wheel brake cylinder of the rear axle. The brake pressure control system comprises an electronic controller processing wheel sensor signals on the basis of one or more control algorithms and providing, at the output thereof, adjustable flows for electromagnetic valves. Certain electromagnetic valves are open in de-energized condition (SO valves) and other electromagnetic valves are closed in de-energized condition (SG) for controlling the pressure in the wheel brake cylinders during the control mode.
German published Patent Application No. DE 3,136,616 discloses an anti-locking brake system for the wheel brakes of an automotive vehicle of a single- or dual-circuit brake system comprising a control system for controlling the brake pressure in the wheel brake cylinders, employing a 2-way-2-position valve normally switched to passage and being inserted into the common brake conduit of a brake circuit leading to the wheel brake cylinders, which conduit branches into at least two brake channels for associated brake cylinders, with 2-way/2-position valves for individually controllable wheel brake cylinders switched to fluid passage in normal brake events being additionally provided in the brake channels and, per brake circuit, one single 2-way/2-position valves switched to passage in the slip control event being provided in the return flow for the purpose of a pressure decrease of a wheel brake to be controlled.
According to the suggestion of the afore-mentioned German Patent Application, at least one of the brake channels of the brake circuit is in direct communication with a wheel brake cylinder, i.e. with no additional 2-way/2-position valve switched to passage in a normal brake event, with the wheel brake cylinder being associated with the vehicle wheel mostly involved in the total brake effect.
German published Patent Application No. DE 3,136,617, moreover, teaches a brake slip control system for the wheel brakes of an automotive vehicle comprising a control system for controlling the brake pressure in the wheel brake cylinders, wherein an inlet valve normally switched to passage is coupled to the master cylinder for feeding pressure fluid into the wheel brake cylinders, with the brake conduit(s) leading away from the master cylinder being respectively branched into at least two brake channels containing valve elements which, in practical operation, permit an adequate control of the wheel brake cylinders, and with a return flow having at least one outlet valve coupled to a non-pressurized reservoir.
According to the latter-mentioned Patent Application, the valve elements constitute at least one pressure control valve feeding into one of the brake channels at a pressure higher than the pressure in the remaining brake channels, with the one brake channel of elevated pressure being associated with the vehicle wheel of the brake circuit mostly involved in the total brake effect.
In present anti-locking control systems for use with passenger cars, one SO- and one SG-valve will be needed per wheel cylinder to be controlled. Only by way of example, reference is made to German published Patent Application Nos. DE 3,040,561 and DE 3,627,000. In brake pressure control means of that type, it is desirable to reduce the number of electromagnetic valves.